How I add bracket in string variable in TCL file

Question

I have written one TCL script but I have one problem when making a string variable as below:

set a 100
set b \"this is variable[$a]\"

I want b

Answer 1

You just need to escape it:

set a 100
set b "this is variable\[$a\]"

Answer 2

Other possibilities (but escaping the brackets is better):

set b [format {this is variable[%d]} $a]
set b [subst -nocom -noback {this is variable[$a]}]

Documentation: set, format, subst